Complete tasks 1-5: UI cleanup, pie chart fix, log path allowlist, activation hardening

Task 1: Remove ActiveBansSection from JailsPage
- Delete buildBanColumns, fmtTimestamp, ActiveBansSection
- Remove Dialog/Delete/Dismiss imports, ActiveBan type
- Update JSDoc to reflect three sections

Task 2: Remove JailDistributionChart from Dashboard
- Delete import and JSX block from DashboardPage.tsx

Task 3: Fix transparent pie chart (TopCountriesPieChart)
- Add Cell import and per-slice <Cell fill={slice.fill}> children inside <Pie>
- Suppress @typescript-eslint/no-deprecated (recharts v3 types)

Task 4: Allow /config/log as safe log prefix
- Add '/config/log' to _SAFE_LOG_PREFIXES in config_service.py
- Update error message to list both allowed directories

Task 5: Block jail activation on missing filter/logpath
- activate_jail refuses to proceed when filter/logpath issues found
- ActivateJailDialog treats all validation issues as blocking
- Trigger immediate _run_probe after activation in config router
- /api/health now reports fail2ban online/offline from cached probe
- Add TestActivateJailBlocking tests; fix existing tests to mock validation

frontend/src/components/config/ActivateJailDialog.tsx

@@ -177,13 +177,9 @@ export function ActivateJailDialog({
 
   if (!jail) return <></>;
 
-  // Errors block activation; warnings are advisory only.
-  const blockingIssues = validationIssues.filter(
-    (i) => i.field !== "logpath",
-  );
-  const advisoryIssues = validationIssues.filter(
-    (i) => i.field === "logpath",
-  );
+  // All validation issues block activation — logpath errors are now critical.
+  const blockingIssues = validationIssues;
+  const advisoryIssues: JailValidationIssue[] = [];
 
   return (
     <Dialog open={open} onOpenChange={(_ev, data) => { if (!data.open) handleClose(); }}>